Influence of microstructure on the microbial corrosion behaviour of stainless steels

Several stainless steels (Types UNS S30300, S30400, S30403. S31600, S31603 and S42000) with different microstructural characteristics have been used t o study the influence of heat treatments on microbiologically influenced co rrosion (MIC). Biocorrosion and accelerated electrochemical testing was per formed in various microbiological media. Two species of sulphate-reducing b acteria (SRB) have been used in order to ascertain the influence of microst ructure. The morphology of corrosion pits produced in both chloride and chl oride Fills sulphide - SRB metabolites - was inspected by optical and scann ing electron microscopy (SEM) complemented with energy-dispersive X-ray (ED X) analysis. Results have shown different behaviours regarding corrosion re sistance in each case studied. Sensitized austenitic stainless steels were more affected by the presence of aggressive anions and pitting potential (E p) values were mure cathodic than those of as-received state. A corrosion e nhancement is produced by the synergistic action of biogenic sulphides and chloride anions. Fitting corrosion in martensitic stainless steel Type UNS S42000 was found in a biocorrosion test. The pitting morphology is correlat ed to the chemical composition, the microstructure and the electrolyte.